The use of fossil fuel as the combustible fuel in gas turbine engines results in the production of a number of undesirable emissions. One particularly undesirable by-product is nitrogen oxide. Recently, governmental imposed regulations have severely restricted the allowable level of nitrogen oxide being emitted in the exhaust gases produced by the engines.
One combustion method that has proven to reduce nitrogen oxide emission levels is catalytic combustion. While this method is known to be effective, it is only effective over a limited overall fuel/air ratio range of the combustor. Levels of engine operation during part-load or during transient loading periods, have been known to experience much higher and environmentally unacceptable emission levels of nitrogen oxide. In some instances, the use of an assist burner has been used in conjunction with a catalyst bed to extend the overall fuel/air ratio range of the combustor. In order to assist the catalytic combustion process in this range of operation, the use of an assist burner downstream from the catalyst bed has been utilized to extend the overall fuel/air ratio range of the combustor. One such design is disclosed in U.S. Pat. No. 4,432,207, issued to Lewis B. Davis et al, on Feb. 21, 1984. It must be noted that while this design is intended to extend the overall fuel/air ratio range within the combustor by utilizing the assist burner downstream of the catalyst bed, it does not control the emission level of nitrogen oxide of the fuel burned by the auxiliary burner.
The present invention is directed to overcoming one or more of the problems set forth above.